Oil Mining, Subsurface

a method of petroleum extraction that is based on the digging of a system of underground mining excavations. The method is used to mine pools containing high-viscosity oils, or bitumens, and heterogeneous pools of medium-viscosity oil that are no longer productive by other methods. Oil may be mined either by washing or by drainage.

In washing, oil-bearing rock is shattered by, as a rule, drilling and blasting. At the working face, the rock is loaded into underground haulage cars by loading machines. The rock is then conveyed up the shaft to the surface, where it is processed in special installations to remove the petroleum fractions. Combined processing of the mineral raw materials is possible; after the petroleum fractions are removed, the containing rock may be used, for example, as a building material or as raw material for the chemical industry.

In drainage, oil is mined by means of boreholes drilled from previously dug mining excavations. Drainage is used in cases where the crude oil either is mobile or may be rendered mobile artificially, for example, by heating the productive formation. If the crude oil is made mobile by artificial means, the final production may be increased to 50–60 percent, as compared with the 5–6 percent achieved by other methods. Mine wells, which may be vertical, inclined, or horizontal, can be drilled to substantial depths. For example, the PBS–2T underground drill rig makes it possible to drill mine wells that are 300 m long and up to 370 mm in diameter. The oil is gathered in underground storage sumps and then pumped to the surface.

Subsurface oil mining has a number of technological advantages. Productive formations are directly accessible, so that losses of heat-transfer fluids before their injection into the formations are reduced to a minimum. In addition, a higher percentage of the oil in a formation is extracted, and fuller use is made of petroleum reserves. Finally, weather conditions do not affect any of the operations. However, subsurface oil mining requires that personnel work underground. Such mining is complicated by the presence of gas shows, a gas cap, bottom water or edgewater, and productive formations composed of loose ground or of quicksand.

In the USSR, the largest amount of experience in subsurface oil mining has been accumulated at the Iarega deposit in the Komi ASSR, where commercial subsurface oil mining has been carried out since 1939. The method of using a heat-transfer fluid to heat the deposit’s productive formation has been tried and developed there since 1968. Mining conditions permit subsurface oil mining at certain fields in Azerbaijan, Kazakhstan, Groznyi Oblast (the Chechen-Ingush ASSR), and Krasnodar Krai.